KR101080351B1 - Display device and driving method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device and a driving method thereof, the display device comprising: a light emitting element, a storage capacitor, a driving transistor for supplying a driving current to the light emitting element, and a first switching transistor for supplying a data voltage according to a scan signal. And a plurality of pixels each including a second switching transistor for diode-connecting the driving transistor according to a shear scan signal, and a third switching transistor for supplying a driving voltage to the driving transistor according to a light emitting signal. In this case, the storage capacitor stores a control voltage depending on the threshold voltage of the driving transistor and the threshold voltage of the light emitting device through the diode-connected driving transistor, and transfers the control voltage and the data voltage to the control terminal of the driving transistor. According to the present invention, even if the threshold voltages of the driving transistor and the organic light emitting diode are changed, the image quality can be prevented by compensating for this.

Display Device, Organic Light Emitting Diode, Thin Film Transistor, Capacitor, Threshold Voltage, Deterioration

Description

Display device and driving method thereof {DISPLAY DEVICE AND DRIVING METHOD THEREOF}

1 is a block diagram of an organic light emitting diode display according to an exemplary embodiment of the present invention.

2 is an equivalent circuit diagram of one pixel of an organic light emitting diode display according to an exemplary embodiment of the present invention.

3 is a cross-sectional view illustrating a driving transistor and an organic light emitting diode of one pixel of an organic light emitting diode display according to an exemplary embodiment of the present invention.

4 is a schematic diagram of an organic light emitting diode of an organic light emitting diode display according to an exemplary embodiment.

5 is an example of a timing diagram illustrating driving signals of an organic light emitting diode display according to an exemplary embodiment of the present invention.

6A through 6D are equivalent circuit diagrams for one pixel in each section shown in FIG. 5.

7 is an equivalent circuit diagram of one pixel of an organic light emitting diode display according to another exemplary embodiment of the present invention.

8 is an example of a timing diagram illustrating driving signals of an organic light emitting diode display according to another exemplary embodiment of the present invention.

The present invention relates to a display device and a driving method thereof.

In recent years, with the reduction in weight and thickness of personal computers and televisions, display devices are also required to be lighter and thinner, and cathode ray tubes (CRTs) are being replaced by flat panel displays.

Such flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), organic light emitting displays, plasma display panels (PDPs), and the like. There is this.

In general, in an active flat panel display, a plurality of pixels are arranged in a matrix form, and an image is displayed by controlling the light intensity of each pixel according to given luminance information. Among these, an organic light emitting display is a display device that displays an image by electrically exciting and emitting a fluorescent organic material. The organic light emitting display is a self-emission type, has a low power consumption, a wide viewing angle, and a fast response time of pixels. It is easy.

The organic light emitting diode display includes an organic light emitting diode (OLED) and a thin film transistor (TFT) driving the same. The thin film transistor is classified into a polysilicon thin film transistor and an amorphous silicon thin film transistor according to the type of the active layer. The organic light emitting diode display employing the polysilicon thin film transistor has various advantages and thus is widely used. However, the manufacturing process of the thin film transistor is complicated and the cost increases accordingly. In addition, it is difficult to obtain a large screen with such an organic light emitting display device.

On the other hand, an organic light emitting display device employing an amorphous silicon thin film transistor is easy to obtain a large screen, and the number of manufacturing processes is relatively smaller than that of an organic light emitting display device employing a polysilicon thin film transistor. However, as the amorphous silicon thin film transistor continuously supplies a current to the organic light emitting diode, the threshold voltage V _th of the amorphous silicon thin film transistor itself may transition and deteriorate. This causes non-uniform current to flow through the organic light emitting element even when the same data voltage is applied, resulting in deterioration in image quality of the organic light emitting diode display.

On the other hand, the threshold voltage of the organic light emitting element also changes as the current flows for a long time. In the case of the n-type thin film transistor, the organic light emitting diode is positioned at the source side of the thin film transistor, and thus, when the threshold voltage of the organic light emitting diode is deteriorated, the source side voltage of the thin film transistor is changed. As a result, even when the same data voltage is applied to the gate of the thin film transistor, the voltage between the gate and the source of the thin film transistor is fluctuated so that an uneven current flows through the organic light emitting device. This also causes a deterioration in image quality of the OLED display.

Accordingly, an aspect of the present invention is to provide a display device and a method of driving the same, including an amorphous silicon thin film transistor and capable of compensating for threshold voltage degradation of an amorphous silicon thin film transistor and an organic light emitting diode.

According to an aspect of the present invention, a display device includes a light emitting device, a storage capacitor, a control terminal, an input terminal, and an output terminal, and supplies a driving current to the light emitting device so that the light emitting device emits light. A driving transistor, a first switching transistor for supplying a data voltage to the sustain capacitor according to a scanning signal, a second switching transistor for diode-connecting the driving transistor according to a shear scan signal, and a driving voltage to the driving transistor according to a light emission signal. A plurality of pixels each including a third switching transistor for supplying, the sustain capacitor stores a control voltage depending on the threshold voltage of the driving transistor and the threshold voltage of the light emitting device through the diode-connected driving transistor, The control voltage and phase It transfers the data voltage to a control terminal of the driving transistor.

The second switching transistor can connect a control terminal and an input terminal of the driving transistor according to the shear scan signal.

The first switching transistor may connect the sustain capacitor to the data voltage according to the scan signal, and the third switching transistor may connect an input terminal of the driving transistor to the driving voltage according to the light emission signal.

The electronic device may further include a fourth switching transistor configured to connect the sustain capacitor to the reference voltage according to the shear scan signal.

The plurality of pixels may include first and second pixels, and the reference voltage may be applied with different values to the first and second pixels.

It may further include an auxiliary capacitor connected to the holding capacitor and charging and maintaining a predetermined voltage.

The first switching transistor may connect the sustain capacitor to a reference signal according to the scan signal.

The apparatus may further include a scan driver generating the front-end scan signal and the scan signal, a data driver generating the data signal and the reference signal, and a light-emitting driver generating the light emission signal.

The plurality of pixels may include first and second pixels, and the data driver may generate the reference signals having different values and apply them to the first and second pixels.

The apparatus may further include a signal controller configured to control the scan driver, the data driver, and the light emitting driver.

The first to third switching transistors and the driving transistor may include amorphous silicon.

The first to third switching transistors and the driving transistors may be nMOS thin film transistors.

The light emitting device may include an organic light emitting layer.                     

According to another exemplary embodiment of the present invention, a display device includes a light emitting device, an input terminal connected to a driving voltage, an output terminal connected to the light emitting device, and a driving transistor having a control terminal, and operating in response to a scan signal and controlling the driving transistor. A first switching transistor connected between a terminal and a data voltage, the second switching transistor connected between an input terminal and a control terminal of the driving transistor, the second switching transistor connected in response to a light emission signal, and operating in response to a light emission signal. And a third switching transistor connected between the input terminal of the transistor and the driving voltage, and a storage capacitor connected between the control terminal of the driving transistor and the first switching transistor.

The electronic device may further include a fourth switching transistor configured to operate in response to the shear scan signal and connected between the sustain capacitor and the reference voltage.

The auxiliary capacitor may further include an auxiliary capacitor connected between the sustain capacitor and the driving voltage or the reference voltage.

According to another embodiment of the present invention, a driving transistor having a control terminal and first and second terminals, a light emitting element connected to the second terminal of the driving transistor, and a capacitor connected to the control terminal of the driving transistor A driving method of a display device includes: supplying a reference voltage and a driving voltage across the capacitor, connecting a control terminal and a first terminal of the driving transistor, applying a data voltage to the capacitor, and driving the driving voltage. Coupling a first terminal of a transistor to the drive voltage.                     

The connecting of the control terminal and the first terminal of the driving transistor may include blocking the driving voltage.

The applying step may include isolating the first terminal of the driving transistor.

DETAILED DESCRIPTION Embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a part of a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the other part being "right over" but also another part in the middle. On the contrary, when a part is "just above" another part, there is no other part in the middle. In addition, when a part is connected to another part, this includes not only a case where the part is "directly" connected to another part but also a part "connected" through another part.

A display device and a driving method thereof according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

First, an organic light emitting diode display according to an exemplary embodiment of the present invention will be described with reference to FIGS. 1 to 6D.

1 is a block diagram of an organic light emitting diode display according to an exemplary embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of one pixel of the organic light emitting diode display according to an exemplary embodiment of the present invention. 3 is a cross-sectional view illustrating a cross-sectional view of a driving transistor and an organic light emitting diode of a pixel of an organic light emitting diode display according to an exemplary embodiment of the present invention, and FIG. 4 illustrates an organic light emitting diode of an organic light emitting diode display according to an exemplary embodiment of the present invention. It is a schematic diagram of a light emitting element.

As shown in FIG. 1, an organic light emitting diode display according to an exemplary embodiment includes a display panel 300, a scan driver 400, a data driver 500, a light emission driver 700, and a display panel 300 connected thereto. And a signal controller 600 for controlling them.

The display panel 300 is connected to a plurality of signal lines (G ₀ -G _n , D ₁ -D _m , S ₁ -S _n ), a plurality of voltage lines (not shown), and a matrix when viewed in an equivalent circuit. It includes a plurality of pixels arranged in the form of.

The signal line includes a plurality of scan signal lines G ₀ -G _n transmitting scan signals V _{g0 to} V _gn , a data line D ₁ -D _m transferring data signals Vdata, and a light emission signal V _s1. It includes a plurality of light emitting signal lines (S ₁ -S _n ) for transmitting ~ V _sn ). The scan signal lines G ₀ -G _n and the light emission signal lines S ₁ -S _n extend substantially in the row direction, are substantially parallel to each other, and the data lines D ₁ -D _m extend substantially in the column direction, and each Parallel

The voltage line includes a driving voltage line (not shown) that transfers the driving voltage Vdd and a reference voltage line (not shown) that transfers the reference voltage Vref. The driving voltage line and the reference voltage line extend in the row or column direction.

As shown in FIG. 2, each pixel includes a driving transistor Qd, capacitors C1 and C2, an organic light emitting element OLED, and four switching transistors Qs1 to Qs4.

The driving transistor Qd has a control terminal ng, an input terminal nd, and an output terminal ns, and the input terminal nd is connected to the driving voltage Vdd. One terminal n1 of the capacitor C1 is connected to the control terminal ng of the driving transistor Qd, and the other terminal n2 is connected to the switching transistors Qs1 and Qs2. The anode and cathode of the organic light emitting diode OLED are connected between the capacitor C1 and the driving voltage Vdd, respectively, and the output terminal ns of the driving transistor Qd and the common voltage Vss. )

The organic light emitting diode OLED displays an image by emitting light at different intensities according to the magnitude of the current I _OLED supplied by the driving transistor Qd, and the magnitude of the current I _OLED is the size of the driving transistor Qd. It depends on the magnitude of the voltage between the control terminal ng and the output terminal ns.

A switching transistor (Qs1) is connected to a terminal (n2) of the scanning signal lines (G _i), a data voltage (Vdata) and the capacitor (C1), operates in response to the scan signal (V _gi).

The switching transistor Qs2 is connected to the scan signal line G _i-1 at the front end, the reference voltage Vref, and the terminal n2 of the capacitor C1, and the switching transistor Qs3 is the scan signal line G at the front end. _i-1 ) and the control terminal ng and the input terminal nd of the driving transistor Qd, and these transistors Qs2 and Qs3 operate in response to the scan signal V _gi-1 of the previous stage. .

The switching transistor Qs4 is connected between the input terminal nd of the driving transistor Qd and the driving voltage Vdd and operates in response to the light emission signal V _si .

The switching and driving transistors Qs1 to Qs4 and Qd are formed of an n-channel metal oxide semiconductor (nMOS) transistor made of amorphous silicon or polycrystalline silicon. However, these transistors Qs1 to Qs4 and Qd may also be pMOS transistors. In this case, since the pMOS transistor and the nMOS transistor are complementary to each other, the operation, voltage and current of the pMOS transistor are opposite to that of the nMOS transistor. do.

Next, the structure of the driving transistor Qd and the organic light emitting diode OLED of the organic light emitting diode display will be described.

As shown in FIG. 3, a control electrode 124 is formed on the insulating substrate 110. The control terminal electrode 124 is inclined with respect to the surface of the substrate 110 and its inclination angle is 20-80 °.

An insulating layer 140 made of silicon nitride (SiNx) is formed on the control terminal electrode 124.

A semiconductor 154 made of hydrogenated amorphous silicon (amorphous silicon is abbreviated a-Si), polycrystalline silicon, or the like is formed on the insulating layer 140.

On top of the semiconductor 154, ohmic contacts 163 and 165 made of a material such as n + hydrogenated amorphous silicon doped with a high concentration of silicide or n-type impurities are formed.

Side surfaces of the semiconductor 154 and the ohmic contacts 163 and 165 are inclined with an inclination angle of 30-80 degrees.

An output electrode 173 and an input electrode 175 are formed on the ohmic contacts 163 and 165 and the insulating layer 140.

The output terminal electrode 173 and the input terminal electrode 175 are separated from each other and positioned at both sides with respect to the control terminal electrode 124. The control terminal electrode 124, the output terminal electrode 173, and the input terminal electrode 175 together with the semiconductor 154 form a switching transistor Qs5, the channel of which is the output terminal electrode 173 and the input terminal. It is formed in the semiconductor 154 between the electrodes 175.

Like the semiconductor 154 and the like, the output terminal electrode 173 and the input terminal electrode 175 are inclined at an angle of about 30-80 °, respectively.

On the output terminal electrode 173 and the input terminal electrode 175 and the exposed portion of the semiconductor 154, an organic material having excellent planarization characteristics and photosensitivity, plasma enhanced chemical vapor deposition (PECVD) A passivation layer 802 made of a low dielectric constant insulating material such as a-Si: C: O, a-Si: O: F, or silicon nitride (SiNx) is formed.

In the passivation layer 802, a contact hole 183 exposing the output terminal electrode 173 is formed.

The pixel electrode 190 is physically and electrically connected to the output terminal electrode 173 through the contact hole 183 on the passivation layer 802. The pixel electrode 190 may be formed of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO) or a material having excellent reflectivity of aluminum or a silver alloy.

An upper portion of the passivation layer 802 is formed of an organic insulating material or an inorganic insulating material, and a partition 803 is formed to separate the organic light emitting cells. The partition 803 surrounds the edge of the pixel electrode 190 to define a region in which the organic emission layer 70 is to be filled.

An organic emission layer 70 is formed in an area on the pixel electrode 190 surrounded by the partition 803.

As shown in FIG. 4, the organic light emitting layer 70 includes an electron transport layer (ETL) and a hole transport layer (ETL) in order to improve the light emission efficiency by improving the balance between electrons and holes in addition to the light emitting layer (EML). A multi-layered structure including a hole transport layer (HTL), and may also include a separate electron injecting layer (EIL) and a hole injecting layer (HIL).

An auxiliary electrode 272 is formed on the barrier rib 803 in the same pattern as the barrier rib 803 and made of a conductive material having a low specific resistance such as metal. The auxiliary electrode 272 contacts the common electrode 270 formed later, and serves to prevent the signal transmitted to the common electrode 270 from being distorted.

The common electrode 270 to which the common voltage Vss is applied is formed on the partition wall 803, the organic emission layer 70, and the auxiliary electrode 272. The common electrode 270 is made of a transparent conductive material such as ITO or IZO. If the pixel electrode 190 is transparent, the common electrode 270 may be made of a metal including calcium (Ca), barium (Ba), aluminum (Al), and the like.

The opaque pixel electrode 190 and the transparent common electrode 270 are applied to a top emission organic light emitting display device that displays an image in an upper direction of the display panel 300. The opaque common electrode 270 is applied to a bottom emission organic light emitting display device that displays an image in a downward direction of the display panel 300.

The pixel electrode 190, the organic emission layer 70, and the common electrode 270 form an organic light emitting diode (OLED) illustrated in FIG. 2, and the pixel electrode 190 is an anode, and the common electrode 270 is a cathode or a pixel electrode. Reference numeral 190 is a cathode, and the common electrode 270 is an anode. The organic light emitting diode OLED uniquely displays one of three primary colors, for example, red, green, and blue, depending on the organic material forming the emission layer EML, and displays a desired color as a spatial sum of these three primary colors.                     

Referring back to FIG. 1, the scan driver 400 is connected to the scan signal lines G ₀ -G _n of the display panel 300 to turn on the high voltage Von and the turn-off which can turn on the switching transistors Qs 1 to Qs 3. The scan signal V _gi , which is a combination of low voltages Voff, may be applied to the scan signal lines G ₀ -G _n to form a plurality of integrated circuits.

The data driver 500 is connected to the data lines D ₁ -Dm of the display panel 300 to apply a data voltage Vdata representing an image signal to the pixels, and may include a plurality of integrated circuits.

The emission driver 700 is connected to the emission signal lines S ₁ -S _n of the display panel 300 to combine a high voltage Von that can turn on the switching transistor Qs4 and a low voltage Voff that can be turned off. The light emitting signal V _si may be applied to the light emitting signal lines S ₁ -S _n , and may be formed of a plurality of integrated circuits.

The plurality of scan driving integrated circuits, data driving integrated circuits, or light emitting driving integrated circuits may be mounted in a chip carrier package (TCP) (not shown) in the form of a chip to attach the TCP to the display panel 300. These integrated circuit chips may be directly attached onto a glass substrate without using them (chip on glass, COG mounting method), and these integrated circuits may be directly formed on the display panel 300 together with the thin film transistors of pixels.

The signal controller 600 controls operations of the scan driver 400, the data driver 500, and the light emission driver 700.                     

Next, the display operation of the organic light emitting diode display will be described in detail with reference to FIGS. 5 to 6D.

5 is an example of a timing diagram illustrating a driving signal of an organic light emitting diode display according to an exemplary embodiment of the present invention, and FIGS. 6A to 6D are equivalent circuit diagrams of one pixel in each section illustrated in FIG. 5.

The signal controller 600 may control the input image signals R, G, and B and their display from an external graphic controller (not shown), for example, a vertical sync signal V _sync and a horizontal sync signal. (H _sync ), a main clock (MCLK), a data enable signal (DE) is provided. The signal controller 600 properly processes the image signals R, G, and B according to the operating conditions of the display panel 300 based on the input image signals R, G, and B and the input control signal, and scan control signals CONT1. ), The data control signal CONT2 and the light emission control signal CONT3 are generated, and then the scan control signal CONT1 is sent to the scan driver 400, and the data control signal CONT2 and the processed image signal DAT are generated. The light emission control signal CONT3 is emitted to the data driver 500 and the light emission control signal CONT3 is emitted to the light emission driver 700.

The scan control signal CONT1 controls the vertical synchronization start signal STV indicating the start of the output of the high voltage Von, the gate clock signal CPV controlling the output timing of the high voltage Von, and the duration time of the high voltage Von. And a limiting output enable signal OE.

The data control signal CONT2 receives a horizontal synchronization start signal STH indicating the start of input of the image data DAT and a load signal LOAD for applying a corresponding data voltage to the data lines D ₁ -D _m . Include.

In the organic light emitting diode display according to the present exemplary embodiment, in order to display an image on one row, for example, the i-th row of pixels, in addition to the i-th scan signal V _gi , the (i-1) th, i.e., the previous scan signal V _gi-1 ) is also used.

First, when the scan driver 400 makes the voltage value of the scan signal V _gi-1 at the front end high voltage Von according to the scan control signal CONT1 from the signal controller 600, the scan signal line G _{i at the} front end. _The switching transistors Qs2 and Qs3 connected to _-1 are turned on. The scanning signal line voltage value of the switching transistor (Qs1) is connected thereto as a low voltage (Voff) of the scanning signals _(gi V) applied to the (G _i) maintains a turn-off state.

At this time, the voltage value of the light-emitting driving part emission signal (V _si) of 700 is applied to the emit signal line (S _i) according to the emission control signal (CONT3) from the signal controller 600 includes a high voltage (Von), and this switching in accordance Transistor Qs4 remains turned on.

An equivalent circuit of the pixel in this state is shown in FIG. 6A, and this section is called the precharge section TA1. As shown in FIG. 6A, the switching transistor Qs4 may be represented by a resistor r.

Then, one terminal n1 of the capacitor C1 and the control terminal ng of the driving transistor Qd are connected to the driving voltage Vdd through the resistor r, so that these voltages are at the driving voltage Vdd. The voltage drop caused by the resistance r is obtained by subtracting the voltage, and the other terminal n2 of the capacitor C1 is connected to the reference voltage Vref and initialized to the reference voltage Vref, and the capacitor C1 is voltage across both ends. Keep your car. At this time, the driving voltage Vdd is sufficiently high than the output terminal voltage Vns of the driving transistor Qd to the extent that the driving transistor Qd can be turned on.

Therefore, the driving transistor Qd is turned on to supply an arbitrary current to the organic light emitting diode OLED through the output terminal ns, whereby the organic light emitting diode OLED may emit light. However, since the length of the precharge section TA1 is very small compared to one frame, the light emission of the organic light emitting diode OLED in this section TA1 is not visually recognized and has little influence on the luminance to be displayed.

Subsequently, the light emission driver 700 changes the light emission signal V _si to a low voltage Voff according to the light emission control signal CONT3 to turn off the switching transistor Qs4 to start the main charging section TA2. The scan signal V _{gi-1 at the} front end maintains the high voltage Von even in this period TA2, and thus the switching transistors Qs2 and Qs3 remain on.

Then, as shown in FIG. 6B, the driving transistor Qd is separated from the driving voltage Vdd and diode connected. That is, the control terminal ng and the input terminal nd of the driving transistor Qd are separated from the driving voltage Vdd while being connected to each other. Since the control terminal voltage Vng of the driving transistor Qd is sufficiently high, the driving transistor Qd separated from the driving voltage Vdd remains turned on.

Accordingly, the electric charges charged in the terminal n1 of the capacitor C1 charged at the predetermined level in the precharge section TA1 start to be discharged through the driving transistor Qd and the organic light emitting element OLED. The control terminal voltage Vng of Qd is lowered. The voltage drop of the control terminal voltage Vng is equal to the threshold voltage Vth of the driving transistor Qd because the voltage between the control terminal ng and the output terminal ns of the driving transistor Qd is equal to the driving transistor Qd. It continues until no more current flows. In this case, the voltage between the anode and the cathode of the organic light emitting diode OLED becomes the threshold voltage Vto of the organic light emitting diode OLED.

therefore,

Is established, and the voltage Vc charged in the capacitor C1 is

Meets.

From this, it can be seen that the capacitor C1 stores a voltage depending on the threshold voltage Vth of the driving transistor Qd and the threshold voltage Vto of the organic light emitting diode OLED.

After the voltage Vc is charged to the capacitor C1, the scan driver 400 changes the front end scan signal V _gi-1 to a low voltage Voff according to the scan control signal CONT1, thereby switching the transistor. The write-in period TA3 starts by turning off Qs2 and Qs3. The light emission signal V _si maintains the low voltage Voff even in this period TA3, and thus the switching transistor Qs4 maintains the off state.

The data driver 500 sequentially receives and shifts the image data DAT for the pixels in the i-th row according to the data control signal CONT2 from the signal controller 600, and corresponds to each image data DAT. The voltage Vdata is applied to the corresponding data lines D ₁ -D _m .

The scan driver 400 turns on the switching transistor Qs1 by making the voltage value of the scan signal V _{gi a} high voltage Von after a predetermined delay time ΔT elapses from the time of the write period TA3.

Then, as shown in FIG. 6C, the input terminal nd of the driving transistor Qd is opened, and the terminal n2 of the capacitor C1 is connected to the data voltage Vdata. Accordingly, the control terminal voltage Vng of the driving transistor Qd is changed as shown in Equation 3 by the bootstrapping effect of the capacitor C1.

Here, the capacitor and the capacitance of the capacitor have the same sign, and C 'represents the total of the parasitic capacitance formed at the control terminal ng of the driving transistor Qd.

If C1 is considerably larger than C ', the control terminal voltage Vng of the driving transistor Qd can be expressed as Equation 4 below.

As a result, the capacitor C1 keeps the voltage Vc charged in the main charging section TA2 as shown in [Equation 2] in this section TA3, while maintaining the data voltage Vdata of the driving transistor Qd. It serves to transmit to the control terminal (ng).

The capacitor C2 serves to stabilize the voltage of the terminal n2 of the capacitor C1 and the control terminal voltage Vng of the driving transistor Qd. One terminal of the capacitor C2 may be connected to the control terminal ng of the driving transistor Qd instead of the terminal n2 of the capacitor C1, in which case the other of the capacitor C2 connected to the driving voltage Vdd. The terminal may be connected to a terminal having a reference voltage Vref, a common voltage Vss, or a separate constant potential. At this time, [Equation 4] is changed to the following [Equation 5].

Therefore, in this case, since the size of the item including the data voltage Vdata becomes small, appropriate size adjustment is required when processing the image signal to display a desired luminance.

In addition, the capacitor C2 may be omitted as necessary.

The light emission driver 700 turns on the switching transistor Qs4 by changing the light emission signal V _si to a high voltage Von according to the light emission control signal CONT3 from the signal controller 600, and then turns on the scan driver 400. The light emission section TA4 is started by turning off the switching transistor Qs1 by changing the scan signal V _gi to the low voltage Voff according to the scan control signal CONT1 from the signal controller 600. Since the scan signal V _{gi-1 at the} front end keeps the low voltage Voff even in this period TA4, the switching transistors Qs2 and Qs3 are kept in the off state.

Then, as shown in FIG. 6D, the terminal n2 of the capacitor C1 is separated from the data voltage Vdata, and the driving voltage Vdd is connected to the input terminal nd of the driving transistor Qd. In this state, there is no outflow and inflow of charge in the capacitor C1, and the capacitor C1 continues to maintain the charged voltage Vc, and the control terminal voltage Vng of the driving transistor Qd is also expressed by Equation 4 Maintain the voltage at].

Accordingly, the driving transistor Qd outputs the output current I _OLED controlled by the voltage Vgs between the control terminal voltage Vng and the output terminal voltage Vns of the driving transistor Qd. Supply to the organic light emitting device (OLED) through. Accordingly, the organic light emitting diode OLED emits light of varying intensity depending on the size of the output current I _OLED to display a corresponding image. The output current I _OLED can be expressed as follows.

Where k is a constant depending on the characteristics of the thin film transistor, where k = μC _SiNxW / L, μ is the field effect mobility, C _SiNx is the capacitance of the insulating layer, W is the channel width of the thin film transistor, and L is The channel length of the thin film transistor is shown.

According to Equations 4 and 6, the output current I _OLED affects the change of the threshold voltage Vth of the driving transistor Qd and the threshold voltage Vto of the organic light emitting diode OLED. Do not receive. That is, if the threshold voltage Vth of the driving transistor Qd is changed by ΔVth or the threshold voltage Vto of the organic light emitting element is changed by ΔVto, the change amount ΔVth, The voltage Vng including ΔVto is charged. Therefore, the variations ΔVth and ΔVto are included in the items Vng, Vth, and Vns in Equation 6 to be erased, and thus the output current I _OLED does not change. As a result, the organic light emitting diode display according to the present exemplary embodiment may compensate for the degradation of the threshold voltage Vth of the driving transistor Qd and the threshold voltage Vto of the organic light emitting diode OLED.

On the other hand, the organic light emitting element OLED may be previously emitted by turning on the switching transistor Qs4 by changing the light emission signal V _si to a high voltage Von in the write period TA3 as necessary. In this case, however, it is preferable to turn off the switching transistor Qs3 and then turn on the switching transistor Qs4.

The light emitting period TA4 continues until the precharge period TA1 for the pixel in the i-th row starts again in the next frame, and the operation in each of the above-described periods TA1 to TA4 is also performed for the pixels in the next row. Repeat the same. In this manner, the sections TA1 to TA4 are sequentially controlled on all the scan signal lines G ₀ -G _n and the emission signal lines S ₁ -S _n to display the corresponding image on all the pixels. Here, the scan signal line G ₀ and the scan signal V _g0 are used only for displaying an image in the pixels of the first row.

The length of each section TA1-TA4 can be adjusted as needed.

The reference voltage Vref may be set at the same voltage level as the common voltage Vss, for example, 0V. Alternatively, the reference voltage Vref may be set to have a negative voltage level. As a result, the data driver 500 may drive the data voltage Vdata to the pixel. Alternatively, the overall luminance of the display panel 300 may be adjusted by adjusting the reference voltage Vref according to the characteristics of the display panel 300.

In particular, as the size of the display panel 300 increases, the driving voltage Vdd may appear differently in the row or column direction due to the resistance of the driving voltage line. In this case, when the reference voltage Vref is applied differently for each row or column, The luminance of the display panel 300 may be uniformly adjusted as a whole.

The driving voltage Vdd is preferably set to a voltage high enough to supply sufficient charge to the capacitor Cst and allow the driving transistor Qd to flow the output current I _OLED .

Next, an organic light emitting diode display according to another exemplary embodiment will be described with reference to FIG. 7.

7 is an equivalent circuit diagram of one pixel of an organic light emitting diode display according to another exemplary embodiment of the present invention.

As illustrated in FIG. 7, each pixel of an organic light emitting diode display according to another exemplary embodiment of the present invention may include a driving transistor Qd, capacitors C1 and C2, an organic light emitting diode OLED, and three switching transistors Qs1 and Qs3. , Qs4).

Since the pixel shown in FIG. 7 is substantially the same as that of the pixel shown in FIG. 2 with the switching transistor Qs2 removed, a detailed description thereof will be omitted.

Next, the display operation of the organic light emitting diode display will be described in detail with reference to FIG. 8.

8 is an example of a timing diagram illustrating driving signals of an organic light emitting diode display according to another exemplary embodiment of the present invention.

In the organic light emitting diode display according to the present exemplary embodiment, in order to display an image on one row, for example, the i-th row of pixels, in addition to the i-th scan signal V _gi , the (i-1) th, i.e., the previous scan signal V _gi-1 ) is also used and supplies not only the data voltage Vdata but also the reference voltage Vref through the data line D _j .

As shown in FIG. 8, the light emission driver 700 applies the voltage value of the light emission signal V _si applied to the light emission signal line S _i according to the light emission control signal CONT3 from the signal controller 600 to the low voltage Voff. to be made by turning the switching transistor (Qs4) connected to a light-emitting signal lines (S _i) to start off the preliminary period (TB1).

Scanning signal (V _gi) so to keep the low-voltage (Voff) in the period (TB1) the switching transistor (Qs1) is connected to the scanning signal lines (G _i) is maintained in an OFF state.

Then, the scan driver 400 makes the voltage value of the scan signal V _gi-1 at the front end high voltage Von according to the scan control signal CONT1 from the signal controller 600, and then, again after a predetermined time, the low voltage ( Voff).

After the previous scan signal V _gi-1 becomes the low voltage Voff, the light emission driver 700 adjusts the voltage value of the light emission signal V _si according to the light emission control signal CONT3 from the signal controller 600. The high voltage Von is turned on to turn on the switching transistor Qs4.

The scanning signal V _gi-1 and the data voltage Vdata at the front end in this section TB1 are used to display an image in the pixels of the (i-1) th row and the (i-2) th row. Therefore, in this section TB1, the effect that the scan signal V _gi-1 and the data voltage Vdata at the front end may have on the pixels in the i-th row rather than to perform the display operation on the pixels in the i-th row is substantially. It is a section set to remove. That is, even if the front end scan signal V _gi-1 becomes the high voltage Von and the switching transistor Qs3 connected to the front end scan signal line Gi _-1 is turned on, the switching transistor Qs4 is turned off. Therefore, the driving voltage Vdd is cut off from the driving transistor Qd. In addition, since the switching transistor Qs1 is turned off, the data voltage Vdata of the reference voltage Vref and the (i-2) th row is not transmitted to the capacitor C1. Accordingly, the control terminal voltage Vng of the driving transistor Qd does not change, and thus does not affect the image display of the i-th row.

The data driver 500 applies the reference voltage Vref to the data lines D ₁ -D _m when the preliminary section TB1 ends.

Subsequently, the scan driver 400 switches the voltage values of the scan signal V _gi-1 and the scan signal V _gi to the high voltage Von according to the scan control signal CONT1 from the signal controller 600. The precharge section TB2 is started by turning on the transistors Qs1 and Qs3, respectively.

Since the light emission signal V _si maintains the high voltage Von, the switching transistor Qs4 remains on. Alternatively, if necessary, the switching transistor Qs4 may be turned on at the start of the precharge period TB2 instead of in the preliminary period TB1.

In the precharge period TB2, except that the switching transistor Qs1 is turned on so that the reference voltage Vref is applied to the terminal n2 of the capacitor C1 through the data lines D ₁ -D _m . Since the operation is substantially the same as the operation in the precharge section TA1 in the foregoing embodiment, a detailed description thereof will be omitted.

The light emission driver 700 changes the light emission signal V _si to a low voltage Voff and turns off the switching transistor Qs4 according to the light emission control signal CONT3 from the signal controller 600, thereby turning on the switching transistor Q3. It begins. Scanning signal (V _gi-1) and the scanning signal (V _gi) of the front end is in the interval (TB3), so to keep the high voltage (Von) switching transistor (Qs1, Qs3) maintains the on state.

Accordingly, the capacitor C1 charges the voltage Vc in [Equation 2]. Since the operation of charging the voltage Vc in this section TB3 is substantially the same as that in the main charging section TA2 of the foregoing embodiment, detailed description thereof will be omitted.

After a predetermined time elapses, the scan driver 400 turns off the switching transistor Qs1 by changing the scan signal V _gi to a low voltage Voff according to the scan control signal CONT1 from the signal controller 600. Then, even if the data driver 500 applies the data voltage Vdata for the image display of the (i-1) th row to the data lines D ₁ -D _m , the pixels in the i th row are not affected. .

In addition, after a predetermined time has elapsed, the scan driver 400 makes the scan signal V _gi-1 of the front end low voltage Voff according to the scan control signal CONT1 from the signal controller 600, and then the data driver ( 500 applies the reference voltage Vref to the data lines D ₁ -D _m in accordance with the data control signal CONT2 from the signal controller 600.

Following the scan driver 400, the signal controller 600 scans the scanning signal make the voltage value of (V _gi) at a high voltage (Von), the switching transistor (Qs1) in response to a control signal (CONT1) by turning on the write interval of from ( TB4) begins.

Since the scan signal V _gi-1 and the light emission signal V _si at the front end maintain the low voltage Voff in this period TB4, the switching transistors Qs3 and Qs4 maintain the off state.

When the write period TB4 starts, the reference voltage Vref is applied to the terminal n2 of the capacitor C1. The reference voltage Vref is for the display operation of the next row i + 1, and the voltage charged by the capacitor C1 even when the reference voltage Vref is applied to the terminal n2 of the capacitor C1 ( Vc) and the control terminal voltage Vng are not affected.

After a predetermined time elapses, the data driver 500 applies the data voltage Vdata of the i-th row to the data lines D ₁ -D _m in accordance with the data control signal CONT2 from the signal controller 600. Accordingly, the capacitor C1 transfers this data voltage Vdata to the control terminal ng of the driving transistor Qd, and maintains the voltage Vng in [Equation 4].

Since the write operation of the data voltage Vdata is substantially the same as the write operation in the write period TA3 of the foregoing embodiment, a detailed description thereof will be omitted.

The light emission driver 700 turns on the switching transistor Qs4 by changing the light emission signal V _si to a high voltage Von according to the light emission control signal CONT3 from the signal controller 600, and the scan driver 400 turns on the switching transistor Qs4. The light emission period TB5 is started by turning off the switching transistor Qs1 by changing the scan signal V _gi to the low voltage Voff according to the scan control signal CONT1 from the signal controller 600. Since the scan signal V _{gi-1 at the} front end keeps the low voltage Voff even in this period TB5, the switching transistor Qs3 is kept in the off state.

Since the display operation in this section TB5 is substantially the same as the display operation in the light emitting section TA4 of the foregoing embodiment, detailed description thereof will be omitted.

As a result, in the organic light emitting diode display according to the present exemplary embodiment, since the control terminal voltage Vng of the driving transistor Qd satisfies Equation 4 during the light emitting period TB5, the threshold voltage Vth of the driving transistor Qd Even if the threshold voltage Vto of the organic light emitting diode OLED is deteriorated, it may be compensated.

In addition, the organic light emitting diode display according to the present exemplary embodiment may reduce the number of switching transistors and wirings by applying the reference voltage Vref through the data driver 500. In addition, since the reference voltage Vref may be applied differently for each row, column, or pixel, the luminance of the display panel 300 may be adjusted more uniformly as a whole.

As described above, three switching transistors, one driving transistor, an organic light emitting element, and a capacitor are provided to store a voltage in the capacitor depending on the threshold voltage of the driving transistor and the threshold voltage of the organic light emitting element. Even if the threshold voltage fluctuates, it can compensate for this and prevent deterioration of image quality.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (20)

Light emitting element, A holding capacitor comprising a first terminal and a second terminal, A driving transistor having a control terminal, an input terminal and an output terminal, and supplying a driving current to the light emitting element so that the light emitting element emits light; A first switching transistor configured to supply a data voltage to a first terminal of the sustain capacitor according to a scan signal; A second switching transistor for diode-connecting the driving transistor according to a shear scan signal, and A third switching transistor supplying a driving voltage to the driving transistor in accordance with a light emission signal A plurality of pixels each including Including; The second terminal of the sustain capacitor is connected to the control terminal of the driving transistor, and the sustain capacitor stores a control voltage depending on the threshold voltage of the driving transistor and the threshold voltage of the light emitting device through the diode-connected driving transistor. And transfer the control voltage and the data voltage to a control terminal of the driving transistor. Display device. In claim 1, And the second switching transistor connects a control terminal and an input terminal of the driving transistor according to the shear scan signal. 3. The method of claim 2, The first switching transistor connects a first terminal of the sustain capacitor to the data voltage according to the scan signal, and a third switching transistor connects an input terminal of the driving transistor to the drive voltage according to the light emission signal. Device. 4. The method of claim 3, And a fourth switching transistor configured to connect the first terminal of the sustain capacitor to a reference voltage according to the shear scan signal. In claim 4, The plurality of pixels include first and second pixels, and the reference voltage is applied with different values to the first and second pixels. 4. The method of claim 3, And an auxiliary capacitor connected to the first terminal of the sustain capacitor and configured to charge and maintain a predetermined voltage. delete delete delete delete delete 4. The method of claim 3, The first to third switching transistors and the driving transistors include amorphous silicon. 4. The method of claim 3, The first to third switching transistors and the driving transistors are nMOS thin film transistors. 4. The method of claim 3, The light emitting device includes an organic light emitting layer. delete delete delete delete delete delete

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